Optimal warm-up stimuli of muscle activation to enhance short and long-term acute jumping performance

The aim of this study was to determine the effect of different types of active warm-up stimuli of muscle activation on explosive jumping performance after short (5 min postwarm-up) and long (6 h postwarm-up) recovery periods following warm-up. Twelve trained volleyball players (21-24 years) performed different types of specific warm-up stimuli (WP) after baseline measurements [e.g., countermovement jump (CMJ) without and with extra load and Drop jump (DJ)] on randomized separate occasions: (1) three sets of five jumps with extra load (WP1), (2) two sets of four reps at 80% of 1RM parallel squat (1RM_PS) and two sets of two reps at 85% of 1RM_PS (WP2), (3) two sets of four reps at 80% of 1RM_PS and two sets of two reps at 90% of 1RM_PS and two sets of one rep at 95% of 1RM_PS (WP3), (4) three sets of five DJs (WP4), (5) specified warm-up for a volleyball match (WP5), (6) three sets of five reps at 30% 1RM_PS (WP6), and (7) an experimental condition of no active warm-up. Height in DJ significantly improved (P < 0.05) after WP1 (4.18%), WP2 (2.98%), WP3 (5.47%), and WP5 (4.49%). Maximal power output during CMJ with extra load significantly improved (P < 0.05) after WP2 (11.39%), WP5 (10.90%), WP3 (9%), and WP1 (2.47%). High-intensity dynamic loading (e.g., 80–95% 1RM), as well as specific volleyball warm-up protocol bring about the greatest effects on subsequent neuromuscular explosive responses. Acute positive effects on jumping performance after warm-up were maintained after long recovery periods (e.g., 6 h following warm-up), particularly when prior high-intensity dynamic actions were performed.     

Timing differences in the generation of ground reaction forces between the initial and secondary landing phases of the drop vertical jump

Background

Rapid impulse loads imparted on the lower extremity from ground contact when landing from a jump may contribute to ACL injury prevalence in female athletes. The drop jump and drop landing tasks enacted in the first and second landings of drop vertical jumps, respectively, have been shown to elicit separate neuromechanical responses. We examined the first and second landings of a drop vertical jump for differences in landing phase duration, time to peak force, and rate of force development.

Methods

239 adolescent female basketball players completed drop vertical jumps from an initial height of 31 cm. In-ground force platforms and a three dimensional motion capture system recorded force and positional data for each trial.

Findings

Between the first and second landing, rate of force development experienced no change (P > 0.62), landing phase duration decreased (P = 0.01), and time to peak ground reaction force increased (P < 0.01). Side-by-side asymmetry in rate of force development was not present in either landing (P > 0.12).

Interpretation

The current results have important implications for the future assessment of ACL injury risk behaviors. Rate of force development remained unchanged between first and second landings from equivalent fall height, while time to peak reaction force increased during the second landing. Neither factor was dependent on the total time duration of landing phase, which decreased during the second landing. Shorter time to peak force may increase ligament strain and better represent the abrupt joint loading that is associated with ACL injury risk.     

Acute effects of different volumes of dynamic stretching on vertical jump performance,flexibility and muscular endurance

The purpose of this study was to examine the acute effects of different volumes of a dynamic stretching routine on vertical jump (VJ) performance, flexibility and muscular endurance (ME). Twenty‐six males (age 22·2 ± 1·3 years) performed three separate randomized conditions: (i) a control (CON) condition (5‐min jog + 12 min of resting), (ii) a 5‐min jog + a dynamic stretching routine (DS1; 6·7 ± 1·3 min) and (iii) a 5‐min jog + a dynamic stretching routine with twice the volume (DS2; 12·1 ± 1·6 min). The dynamic stretching routine included 11 exercises targeting the hip and thigh musculature. VJ performance (jump height and velocity) and flexibility were measured prior to and following all conditions, while ME was measured following all conditions. The DS1 and DS2 conditions increased VJ height and velocity (P<0·01), while the CON condition did not change (P>0·05). When compared to the CON condition, the DS1 condition did not improve ME (P>0·05), whereas the DS2 condition resulted in a significant (15·6%) decrease in the number of repetitions completed (P<0·05). Flexibility increased following all conditions (P<0·01), while the DS1 condition was significantly greater (P<0·01) than the CON condition at post‐testing. These results suggest that dynamic stretching routines lasting approximately 6–12 min performed following a 5‐min jog resulted in similar increases in VJ performance and flexibility. However, longer durations of dynamic stretching routines may impair repetitive high‐intensity activities.     

Less conservative stabilization conditions for Markovian jump systems with incomplete knowledge of transition probabilities and input saturation

This paper proposes less conservative stabilization conditions for Markovian jump systems with incomplete knowledge of transition probabilities and input saturation. The transition rates associated with the transition probabilities are expressed in terms of three properties, which do not require the lower and upper bounds of the transition rates, differently from other approaches in the literature. The resulting conditions are converted into the second‐order matrix polynomial of the unknown transition rates. The polynomial can be represented as quadratic form of vectorized identity matrices scaled by one and the unknown transition rates. And then, the LMI conditions are obtained from the quadratic form. Also, an optimization problem is formulated to find the largest estimate of the domain of attraction in mean square sense of the closed‐loop systems. Finally, two numerical examples are provided to illustrate the effectiveness of the derived stabilization conditions. Copyright © 2016 John Wiley & Sons, Ltd.     

Optimal guaranteed cost synchronization of coupled neural networks with Markovian jump and mode‐dependent mixed time‐delay

This paper is concerned with the optimal guaranteed cost synchronization problem for a class of coupled neural networks with Markovian jump parameters and mode‐dependent mixed time‐delay. The coupled neural networks contained N‐identical delayed neural nodes and M switch modes from one mode to another according to a Markovian chaining with known transition probability. All the coupled networks' parameters covering the coupled matrix and discrete and distributed time‐delay also depend on the Markovian jump mode. The associated optimal guaranteed cost function is a quadratic function; the activation function is supposed to satisfy sector‐bounded condition. By employing a new Lyapunov–Krasovskii functional and some analytic skills, the sufficiency conditions of guaranteed cost synchronization are derived to ensure that coupling neural network is asymptotically synchronized for related cost function in mean square. The exported sufficient condition is closely contacted with the distributed time‐delay, the mode transition probability, the discrete‐time delay, and the coupled structure of networks. The achieved conditions are given in the light of LMI that can be usefully solved by using the semi‐definite program scheme. Moreover, an LMI‐based approach to export the guaranteed cost synchronization controller is formulated to minimize the optimal guaranteed cost for closed‐loop dynamical networks. Numerical simulations are developed to further display the efficiency of the achieved theoretical results. Copyright © 2015 John Wiley & Sons, Ltd.     

Modular thermal sensors in temperature-gated transient receptor potential (TRP) channels

The molecular basis of the thermal sensitivity of temperature-sensitive channels appears to arise from a specific protein domain rather than integration of global thermal effects. Using systematic chimeric analysis, we show that the N-terminal region that connects ankyrin repeats to the first transmembrane segment is crucial for temperature sensing in heat-activated vanilloid receptor channels. Changing this region both transformed temperature-insensitive isoforms into temperature-sensitive channels and significantly perturbed temperature sensing in temperature-sensitive wild-type channels. Swapping other domains such as the transmembrane core, the C terminus, and the rest of the N terminus had little effect on the steepness of temperature dependence. Our results support that thermal transient receptor potential channels contain modular thermal sensors that confer the unprecedentedly strong temperature dependence to these channels.     

RELATIONSHIP BETWEEN HIP STRENGTH AND TRUNK,HIP, AND KNEE KINEMATICS DURING A JUMP‐LANDING TASK IN INDIVIDUALS WITH PATELLOFEMORAL PAIN

Background/Purpose:

Decreased strength of the hip musculature and altered mechanics of the lower extremity have been identified in individuals with patellofemoral pain (PFP). The aim of this study was to determine if a relationship exists between hip muscle strength and transverse and frontal plane motion at the hip and knee, and ipsilateral trunk flexion during a jump‐landing task in individuals with PFP.

Methods:

Fifteen individuals (10 females, 5 males) with PFP participated in this investigation. A three‐dimensional motion analysis system was utilized to assess trunk, hip, and knee kinematics during a jump‐landing task. An isokinetic dynamometer was utilized to assess concentric and eccentric strength of the hip musculature. Simple correlation analyses were performed to determine the relationships between hip muscle strength and peak frontal and transverse plane hip and knee kinematics and ipsilateral trunk flexion.

Results:

Decreased eccentric strength of the hip external rotators and abductors was significantly correlated to increased frontal plane motion at the hip and trunk, respectively (P<0.05).

Conclusions:

Based on these findings, eccentric strengthening exercises for the hip musculature may be an important component for clinicians to include when rehabilitating individuals with PFP who display increased frontal plane motion at the hip and trunk.

Level of Evidence:

2b     

Effects of plyometric training on passive stiffness of gastrocnemii and the musculo‐articular complex of the ankle joint

This study aimed to determine simultaneously the effects of plyometric training on the passive stiffness of the ankle joint musculo‐articular complex, the gastrocnemii muscle–tendon complex (MTC) and the Achilles tendon in order to assess possible local adaptations of elastic properties. Seventeen subjects were divided into a trained (TG) group and a control (CG) group. They were tested before and after 8 weeks of a plyometric training period. The ankle joint range of motion (RoM), the global musculo‐articular passive stiffness of the ankle joint, the maximal passive stiffness of gastrocnemii and the stiffness of the Achilles tendon during isometric plantar flexion were determined. A significant increase in the jump performances of TG relative to CG was found (squat jumps: +17.6%, P=0.008; reactive jumps: +19.8%, P=0.001). No significant effect of plyometric training was observed in the ankle joint RoM, musculo‐articular passive stiffness of the ankle joint or Achilles tendon stiffness (P>0.05). In contrast, the maximal passive stiffness of gastrocnemii of TG increased after plyometric training relative to CG (+33.3%, P=0.001). Thus, a specific adaptation of the gastrocnemii MTC occurred after plyometric training, without affecting the global passive musculo‐articular stiffness of the ankle joint.     

Kinetic studies on the formation and decay of metarhodopsins from bovine retinas

The kinetics of the equilibration of MRI in equilibrium MRII were studied over a range of temperature and pH. Two methods were used to evaluate the relaxation time of this process. The rate of disappearance of MRI or the rate of appearance of MRII were measured after a light flash. The established equilibrium between these two intermediates at low temperatures was subjected to pressure perturbations. This latter technique was used to show that the equilibrium was truly reversible and to determine the relaxation time. From these experiments the equilibrium constants and forward and reverse rate constants were evaluated under different conditions. The simplest interpretation of our results is that the reaction can be described by a single kinetic step. This step involves a conformation change which is accompanied by a change in pK of approx. 3 units of an ionizing group of rhodopsin, resulting in the uptake of a proton during the formation of MRII.     

Pyrrolidine ring conformations in prolyl peptides from 13C spin-lattice relaxation times

A method was developed in the framework of a bistable jump model to obtain the pyrrolidine ring conformations in proline peptides from ¹³C spin-lattice relaxation times. Equations are presented expressing the ring torsions in terms of the ¹³C spin-lattice relaxation times of the ring carbons. This method was applied to 26 pyrrolidine ring systems and acceptable conformations were obtained.